Electric induction furnace



Aug. 1933- A. E. GREENE 1,920,380

ELEGTRI C INDUCTI ON FURNACE Filed March 24, 1932 FaqlL INVENTOR EMMYMMEIZQ ATTORNEY Patented Aug. 1, 1933) UNITED STATES PATENT, OFFICEClaims.

My present invention relates to improvements in inductionfurnaces andparticularly to improvements in construction and in operation wherebyinduction furnaces may be started easily 5 on cold metal without the useof molten metal or without delay in melting cold starting rings, orcircuits. My present invention also relates to improvements in theconstruction of parts of induction furnaces for containing molten metal.1 My present application is a continuation in part ofmy U. S.application for patent Serial No. 323,515 filed Dec. 3, 1928, whichissued as U. S. PatentNo. 1,851,575, which application was in turn acontinuation in part of my U. S. application for patent Serial No.406,894 which issued as U. S. Patent No. 1,751,912 on March 25, 1930;and my Serial No. 455,601 filed March 25, 1921 which issuedas U. S.Patent No. 1,751,856 on March 25, 1930, and of my U. S. application forpatent Serial No. 575,630 filed July 17, 1922 (application abandoned).

Induction furnaces prior to the time of my invention described in thisapplication were not well suited to the melting of cold scrap metal.They did not provide suflicient voltage in the secondary circuit tosatisfactorily overcome the resistancebetween the cold scraps of metaland they did not provide for control of the voltage and of the currentso that a high voltage could be used to melt the cold scrap and then alow voltage induced in the molten metal circuit. Nor did they providefor a positive mechanical circulation of the molten metal where smallarea conduits are part of the secondary single turn molten metal circuitaround a magnetic core.

These earlier furnaces operated at relatively low voltages of 5 to 10volts and in fact many of the V type induction furnaces for brass stilluse such a relatively low voltage. A disadvantage of such furnaces isthat they must be started either very carefully with a cold insert orelse heated and filled with molten metal, and they have a furtherdisadvantage of very limited usefulness when the metal compositionvaries as between red brass and yellow brass and lead containing metal.Another disadvantage of such furnaces as the V type is that theirrefractory linings have to be made with great care and are liable tocrack, and when they do crack they are no longer usable.

In the open ring type induction furnace, there is thedisadvantage of lowsingle turn voltage, poor power factor and inconvenient shape of chargechamber. It has not been possible to throw loose scrap into such afurnace and start it without molten metal or without a special sin glecircuit ring.

My present invention is intended .to obviate these and otherdisadvantages and to provide improved means for starting inductionfurnaces with cold scrap and to avoid the objections of low operatingvoltages and inability to melt metal with a varying conductivity.

My present invention contemplates the use of small area conduitsconnecting with one or more v larger chambers whereby relatively highvoltages may be utilized in the single turn circuit to advantage.

One object of my present invention is an improved construction of thesmall area duct containers so that replacement is simplified and so thatvery thin walls around the duct can be used without danger, and Iaccomplish this improvement by the use of a water cooled channel shellfor this part of the secondary circuit. A further object of my inventionis the provision of improved insulation of the shell parts of thefurnace. Another object of my invention is an improved constructionwhereby a plurality of conduits can be used between enlarged chambers sothat polyphase alternating current can be used advantageously. A stilldifferent object of my invention is an improved construction of chambersand ducts whereby straight metal bars may be inserted and utilized forstarting the circuit thru the channels to avoid the necessity ofstarting with molten metal or with a solid closed ring circuit. Theseand other objects of my invention will be better understood by referenceto the annexed drawing. 90

In the annexed drawing I have shown in Fig.

1 a sectional elevation view of an embodiment of my invention in whichstarting bars of metal are used between two chambers having electrodesand also means for inducing current thru the 95 bars and charge in thechambers.

Fig. 2 is a plan view of the furnace shown in Fig. 1 in part showing twoof the tubes and a part of the third core.

Fig. 3 is a sectional elevation view of another modification of myinvention in which a main chamber is provided with a horizontal arebetween two horizontal adjustable electrodes, and induction heatingmeans combined therewith.

Fig. 4 is a sectional elevation view thru the electrodes of the arcchamber of Fig. 3.

Fig. 5 is a wiring diagram of the circuits and diagrammatic view of thesecondary circuits of the furnace of Fig. 3 and Fig. 4.

Fig. 6 is a sectional plan view of a water-cooled tube for the secondarycircuit, embodying my invention, and Fig 7 is a sectional view of thistube.

Referring to this drawing and particularly to Figs. 1 and 2, I haveillustrated here an induction furnace which embodies my improvement forstarting the induction heating by means of metal bars which can beinserted into the tubes so as to make a. circuit between the scrap inthe two enlarged chambers. The two chambers are shown at 1 and 2 withtop adjustable electrodes, 3 and 4, for arcing to or contacting with thecharge. I have shown cold scrap charge at 7 and 3 resting on each end ofthe bar 6 which extends from one chamber to the other. The refractory ofthe main chambers is indicated at 5. The bar 6 extends thru the tubemarked 19 in Fig. 2 where the tube is shown in dotted lines. The ends ofthe bar 6 are shown in Fig. 2 in each chamber. The cold scrap is notshown in the Fig. 2 illustration. A magnetic core 9 in Fig. 1 withvertical legs marked 12 in Fig. 2 encircles the bar 6. Two windings, l0and 11 on this core are indicated in Fig. 1. One of these may beconnected to the supply and the other to the electrode circuit in thefurnace. In this way heating may be applied thru the electrodes and thruthe bar '6 whereby the bar and the two electrodes form a single circuitof any suitable number of turns of winding around the magnetic core andswitching means may be provided for adjustment of the electrode circuitvoltage independently of the single turn circuit voltage. I have shownseparate cores encircling each tube, the core 13 encircling tube 20 thruwhich a bar 18 is indicated, and another core 14 is shown in part for athird tube, for example where three phase power is used.

It will be noted that I have provided separate cores and windingsthereon above the tubes. This is one particular feature of my inventionAnother feature is the provision for the use of the metal bars. The bar6 is inserted thru the opening 15 and then the opening or tap hole 15 issubseqently closed by a plug of refractory material. The ends of the bar6 extend into both chambers. Scrap may then be placed on the ends of thebar 6 and other bars such as 13, thus forming a circuit from one chamberto the other. With sufliciently high single turn voltage and sufficientweight of scrap on the ends of the bars, current can be induced thru thebars and loose scrap until the charge melts. If the circuit is broken,the electrode may be used and an arcing voltage applied thru theelectrodes to the charge and thence to the bars and thru the coil on thecore. The weight of the scrap is sometimes not sufiicient for quickstarting and then the electrode circuit is used. The electrode circuitmay be used in any event. The voltage available from the coils on thecore is ample for both the high single turn circuits and for the arcingcircuits and adjustment of both voltages may be provided by taps on thecoils on the core.

As mentioned in my earlier applications, in

-melting nonferrous metal such as brass, I may use a bar of copper inthe tubes or of metal of different melting point from that to be meltedin the main chambers, and may use a metal of either lower or highermelting point for the bars than the scrap to be melted. The startingbars melt up in the operation and new bars are provided for startingfrom the cold.

In Figs. 3, 4 and 5 I have illustrated a modification of my invention inwhich a horizontal arc is combined with an induction circuit. In thisfurnace a main chamber 31 is provided connecting with an induction tubecircuit in which the tube 34 is one part and the reservoir 35 connectstherewith at the part opposite the main chamber so that the furnace maybe rocked. The rocking means is not shown, but it is understood thatthis as well as the furnace of Fig. 1 may be mounted for tilting orrocking movement and for circulation of metal from the one chamber, like31 into the reservoir 35 and back. The magnetic core is shown at 41 and42. Coils 43 and 44 are mounted on the core, and coil 44 is arrangedwith taps for connection to a supply circuit of single phase power, andcoil 43 is arranged, also with taps, to supply current to the arccircuit between the electrodes 37 and 32. In Fig. 5 I have shown acircuit diagram of this furnace. Primary coil 44 has taps for theadjustment of the induced voltage. Coil 43 serves to supply differentvoltages to the electrodes. The are is indicated at 38 and the inductionsecondary single turn circuit at 48. The voltage of this circuit isadjustable by the taps on coil 44.

This furnace provides means for heating the metal by induction and forheating the slag by means of a horizontal are above the slag which mayform on the metal. It is a special purpose of my invention to providethis combined means for heating both metal and slag, and for keeping theelectrodes away from the metal, as for example in the melting of verylow carbon metal.

Figs. 6 and 7 show a water cooled induction tube member such as might beused at 19 or 20 in Fig. 2 or at 36 in Fig. 3. In this water cooledtube, I have provided a metal shell 68 inside of which is a refractorymaterial forming a tube or conduit 61. This conduit forms the containerfor the molten metal of the induction circuit. Around the metal 68 is anouter metal wall 67 so arranged that it holds water and that water maybe circulated thru the cooling chamber 64. I have shown an inlet 63 andan outlet 65 for water. I have also provided for a joint of insulatingmaterial so that a complete circuit around the tube is avoided. I mayuse insulating material such as Transits for this purpose. Thisinsulating member is shown at 69 in Fig. 6 and the two parts of theshell are held against the transits by bolts as shown at 70. I have alsoindicated the refractory joint between the tube shell and the furnaceshell, the latter being indicated in section at '73 and '76. Insulationmembersare shown at 71 and '72 between the metal of the furnace shelland that the tube shell so as to prevent induced current from passing inthis direction. The refractory material of the main furnace is indicatedat 74 and the continuation of the conduit 61 is-shown at '75 in the mainchamber refractory. The refractory of the tube and that of the mainshell are pressed together and held together by suitable structuralbolting members not shown.

My invention is an improvement in many ways over past construction andmethods of operation. By means of the bars it is easy to start theinduction circuit without molten metal from an outside source and yetthe furnace need not retain any molten metal from one heat to another.The electrode circuits provide for heating of the slag independently ofthe metal and in other modifications I provide for using induced currentwhich may be passed from one electrode to another thru a bar or tube ofmetal in order to start the melting of the loose scrap in the enlargedchambers.

My water cooled tube construction provides means for small refractorymembers so that the core of the induction furnace can be a comparativelyshort one and thus provide for high powerfactors. The location ofwindings above the tubes and on separate magnetic cores is likewise anadvantage for electric operation since it places the coils in aconvenient place and by means of the separate cores, one for each tube,I am able to remove and replace tubes independently of each other.

What I claim is:-

1. In an induction furnace comprising a straight channel section as partof the single turn induction circuit, said straight section connectingwith two larger chambers having adjustable electrodes entering fromabove, means for inserting a bar thru the straight channel so as toextend into both the larger chambers, whereby a circuit can be completedfrom one electrode thru the bar to the other electrode.

2. In an induction furnace comprising one or more straight channelsections forming part of the secondary circuit and having a relativelysmall cross sectional area, means for inserting a bar of metal in thestraight channels, means for closing the hole for inserting said barinto said channels so that the metal will not run out when molten, andmeans for inducing current thru said bar to cause it to melt.

3. An induction furnace comprising two'enlarged chambers in refractorymaterial and ducts in refractory material between said chambers, saidducts having a relatively small cross sectional area and joining thechambers at the lower parts of said chambers, means for inserting metalbars in said ducts so that the ends of said bars will extend into thechambers at both ends of the bars, and means for causing a current topass thru the bars by the use of sufficiently high voltage to cause themto melt and to maintain a secondary circuit thru them and molten metalin the enlarged chambers.

4. In an induction furnace, two enlarged chambers in refractory materialfor holding loose metal charge, two or more small area conduits inrefractory material joining said enlarged chambers at their lower parts,means for placing straight starting metal bars in said conduits so thattheir ends will make contact with the loose scrap in the enlargedchambers, and means for passing current from one enlarged chamber to theother thru said starting bars until the bars are melted and forcontinuing the flow of induced current thru the single turn circuit thusformed around a magnetic core thru the metal in the conduits and theenlarged chambers.

5. In 'an induction furnace comprising one or more enlarged chambers andone or more small area ducts in refractory material connecting with thelarger chambers at different places near the bottom thereof, means forplacing a straight metal bar thru said ducts to make contact with loosescrap in the enlarged chambers, and means for inducing a sufficientlyhigh voltage thru the metal bar and scrap to melt the bar and to permitcontinuing the flow of current, means for rocking the furnace to movethe metal thru said duct, and means for regulating the voltage aroundthe induction circuit.

ALBERT E. GREENE.

